Localization of endogenous lectins in normal human breast, benign breast lesions and mammary carcinomas

Examining Galectin Gene Regulation by Reporter Assays

Matching their role as potent and versatile effectors in cellular homeostasis and disease processes, galectins are subject to a fine-tuned transcriptional regulation of gene expression. It can apparently even involve coregulation with certain elements of the enzymatic machinery for glycan biosynthesis/remodeling and/or functional carriers of galectin-binding glycans such as the α₅β₁-integrin. All this suggests not yet fully known combinatorial processes to reach the desired outcome. Identification of transcription start point(s), cloning of upstream promoter region, and the design of plasmids for luciferase-based reporter assays establish the platform to initiate a systematic search of regulatory sequences. Their elucidation is also a step toward rationally manipulating expression of galectin genes in pathogenesis.

Exploring the Galectin Network by Light and Fluorescence Microscopy

Dynamic changes of a cell's glycophenotype are increasingly interpreted as shifts in the capacity to interact with tissue (endogenous) lectins. The status of glycan branching or chain length (e.g., core 1 vs core 2 mucin-type O-glycans and polyLacNAc additions) as well as of sialylation/sulfation has been delineated to convey signals. They are "read" by galectins, for example regulating lattice formation on the membrane and cell growth. Owing to the discovery of the possibility that these effectors act in networks physiologically resulting in functional antagonism or cooperation, their detection and distribution profiling need to be expanded from an individual (single) protein to the-at best-entire family. How to work with non-cross-reactive antibodies and with the labeled tissue-derived proteins (used as probes) is exemplarily documented for chicken and human galectins including typical activity and specificity controls. This description intends to inspire the systematic (network) study of members of a lectin family and also the application of tissue proteins beyond a single lectin category in lectin histochemistry.

Galectins in Endothelial Cell Biology and Angiogenesis: The Basics

Angiogenesis, the growth of new blood vessels out of existing vessels, is a complex and tightly regulated process. It is executed by the cells that cover the inner surface of the vasculature, i.e., the endothelial cells. During angiogenesis, these cells adopt different phenotypes, which allows them to proliferate and migrate, and to form tube-like structures that eventually result in the generation of a functional neovasculature. Multiple internal and external cues control these processes and the galectin protein family was found to be indispensable for proper execution of angiogenesis. Over the last three decades, several members of this glycan-binding protein family have been linked to endothelial cell functioning and to different steps of the angiogenesis cascade. This review provides a basic overview of our current knowledge regarding galectins in angiogenesis. It covers the main findings with regard to the endothelial expression of galectins and highlights their role in endothelial cell function and biology.

How galectins have become multifunctional proteins

Having identified glycans of cellular glycoconjugates as versatile molecular messages, their recognition by sugar receptors (lectins) is a fundamental mechanism within the flow of biological information. This type of molecular interplay is increasingly revealed to be involved in a wide range of (patho)physiological processes. To do so, it is a vital prerequisite that a lectin (and its expression) can develop more than a single skill, that is the general ability to bind glycans. By studying the example of vertebrate galectins as a model, a total of five relevant characteristics is disclosed: i) access to intra- and extracellular sites, ii) fine-tuned gene regulation (with evidence for co-regulation of counterreceptors) including the existence of variants due to alternative splicing or single nucleotide polymorphisms, iii) specificity to distinct glycans from the glycome with different molecular meaning, iv) binding capacity also to peptide motifs at different sites on the protein and v) diversity of modular architecture. They combine to endow these lectins with the capacity to serve as multi-purpose tools. Underscoring the arising broad-scale significance of tissue lectins, their numbers in terms of known families and group members have steadily grown by respective research that therefore unveiled a well-stocked toolbox. The generation of a network of (ga)lectins by evolutionary diversification affords the opportunity for additive/synergistic or antagonistic interplay in situ, an emerging aspect of (ga)lectin functionality. It warrants close scrutiny. The realization of the enormous potential of combinatorial permutations using the five listed features gives further efforts to understand the rules of functional glycomics/lectinomics a clear direction.

Galectin-3: is this member of a large family of multifunctional lectins (already) a therapeutic target?

Introduction: The discoveries that sugars are a highly versatile platform to generate biochemical messages and that glycan-specific receptors (lectins) are a link between these signals and their bioactivity explain the interest in endogenous lectins such as galectins. Their analysis is a highly dynamic field. It is often referred to as being promising for innovative drug design. Area covered: We present a primer to the concept of the sugar code by glycan-(ga)lectin recognition, followed by a survey on galectin-3 (considering common and distinct features within this family of multifunctional proteins expressed at various cellular sites and cell types). Finally, we discuss strategies capable of blocking (ga)lectin activity, with an eye on current challenges and inherent obstacles. Expert opinion: The emerging broad profile of homeostatic and pathophysiological bioactivities stimulates further efforts to explore galectin (Gal-3) functionality, alone and then in mixtures. Like thoroughly assessing the pros and cons of blocking approaches for a multifunctional protein active at different sites, identifying a clinical situation, in which the galectin is essential in the disease process, will be critical.

Pharmacological activation of estrogen receptors-α and -β differentially modulates keratinocyte differentiation with functional impact on wound healing

Estrogen deprivation is considered responsible for many age-related processes, including poor wound healing. Guided by previous observations that estradiol accelerates re‑epithelialization through estrogen receptor (ER)‑β, in the present study, we examined whether selective ER agonists [4,4',4''-(4-propyl [1H] pyrazole-1,3,5-triyl)‑trisphenol (PPT), ER‑α agonist; 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), ER‑β agonist] affect the expression of basic proliferation and differentiation markers (Ki‑67, keratin‑10, ‑14 and ‑19, galectin‑1 and Sox‑2) of keratinocytes using HaCaT cells. In parallel, ovariectomized rats were treated daily with an ER modulator, and wound tissue was removed 21 days after wounding and routinely processed for basic histological analysis. Our results revealed that the HaCaT keratinocytes expressed both ER‑α and ‑β, and thus are well-suited for studying the effects of ER agonists on epidermal regeneration. The activation of ER‑α produced a protein expression pattern similar to that observed in the control culture, with a moderate expression of Ki‑67 being observed. However, the activation of ER‑β led to an increase in cell proliferation and keratin‑19 expression, as well as a decrease in galectin‑1 expression. Fittingly, in rat wounds treated with the ER‑β agonist (DPN), epidermal regeneration was accelerated. In the present study, we provide information on the mechanisms through which estrogens affect the expression patterns of selected markers, thus modulating keratinocyte proliferation and differentiation; in addition, we demonstrate that the pharmacological activation of ER-α and -β has a direct impact on wound healing.

Introduction to glycopathology: the concept, the tools and the perspectives

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1670639891114983.

Analyzing the flow of biological information is a fundamental challenge for basic sciences. The emerging results will then lend themselves to the development of new approaches for medical applications. Toward this end, the products of protein/lipid glycosylation deserve special attention. The covalent attachment of sugars to these carriers means much more than just a change of the carriers’ physicochemical properties. In principle, the ubiquitous presence of glycoconjugates and the close inspection of the particular structural ‘talents’ of carbohydrates provide suggestive evidence for information coding by sugars. In fact, the theoretical number of ‘words’ (oligomers) formed by ‘letters’ (monosaccharides) is by far higher than by using nucleotides or amino acids. In other words, glycans harbor an unsurpassed coding capacity. The cyto- and histochemical detection of dynamic changes in the profile of cellular glycans (glycome, the equivalent of the proteome) by sugar receptors such as antibodies used as tools underscores the suitability of carbohydrates for such a task. The resulting staining patterns can be likened to a molecular fingerprint. By acting as ligand (counterreceptor) for endogenous receptors (tissue lectins), glycan epitopes become partners in a specific recognition pair, and the sugar-encoded information can then be translated into effects, e.g. in growth regulation. Of note, expression of both sides of such a pair, i.e. lectin and cognate glycan, can physiologically be orchestrated for optimal efficiency. Indeed, examples how to prevent autoimmune diseases by regulatory T cells and restrict carcinoma growth by a tumor suppressor attest occurrence of co-regulation. In consequence, these glycans have potential to establish a new class of functional biomarkers, and mapping presence of their receptors is warranted. In this review, the cyto- and histochemical methods, which contribute to explore information storage and transfer within the sugar code, are described. This introduction to the toolbox is flanked by illustrating the application of each type of tool in histopathology, with focus on adhesion/growth-regulating galectins. Together with an introduction to fundamental principles of the sugar code, the review is designed to guide into this field and to inspire respective research efforts.

The third dimension of reading the sugar code by lectins: design of glycoclusters with cyclic scaffolds as tools with the aim to define correlations between spatial presentation and activity

Coding of biological information is not confined to nucleic acids and proteins. Endowed with the highest level of structural versatility among biomolecules, the glycan chains of cellular glycoconjugates are well-suited to generate molecular messages/signals in a minimum of space. The sequence and shape of oligosaccharides as well as spatial aspects of multivalent presentation are assumed to underlie the natural specificity/selectivity that cellular glycans have for endogenous lectins. In order to eventually unravel structure-activity profiles cyclic scaffolds have been used as platforms to produce glycoclusters and afford valuable tools. Using adhesion/growth-regulatory galectins and the pan-galectin ligand lactose as a model, emerging insights into the potential of cyclodextrins, cyclic peptides, calixarenes and glycophanes for this purpose are presented herein. The systematic testing of lectin panels with spatially defined ligand presentations can be considered as a biomimetic means to help clarify the mechanisms, which lead to the exquisite accuracy at which endogenous lectins select their physiological counterreceptors from the complexity of the cellular glycome.

Context-dependent multifunctionality of galectin-1: a challenge for defining the lectin as therapeutic target

INTRODUCTION

One route of translating the information encoded in the glycan chains of cellular glycoconjugates into physiological effects is via receptor (lectin) binding. A family of endogenous lectins, sharing folding, a distinct sequence signature and affinity for β-galactosides (thus termed galectins), does so effectively in a context-dependent manner.

AREAS COVERED

An overview is given on the multifunctional nature of galectins, with emphasis on galectin-1. The broad range of functions includes vital processes such as adhesion via glycan bridging, glycoconjugate transport or triggering signaling relevant, for example, for growth regulation. Besides distinct glycoconjugates, this lectin can also interact with certain proteins so that it can target counterreceptors at all sites of location, that is, in the cytoplasm and/or nucleus, at both sides of the membrane or extracellularly. Approaches to strategically exploit galectin activities with therapeutic intentions are outlined.

EXPERT OPINION

The wide versatility of sugar coding and the multifunctionality of galectin-1 explain why considering to turn the protein into a therapeutic target is an ambitious aim. Natural pathways shaped by physiologic master regulators (e.g., the tumor suppressor p16(INK4a)) are suggested to teach inspiring lessons as to how the lectin might be recruited to clinical service.

Structure-based optimization of angiostatic agent 6DBF7, an allosteric antagonist of galectin-1

Galectin-1 (gal-1), which binds β-galactoside groups on various cell surface receptors, is crucial to cell adhesion and migration, and is found to be elevated in several cancers. Previously, we reported on 6DBF7, a dibenzofuran (DBF)-based peptidomimetic of the gal-1 antagonist anginex. In the present study, we used a structure-based approach to optimize 6DBF7. Initial NMR studies showed that 6DBF7 binds to gal-1 on one side of the β-sandwich away from the lectin's carbohydrate binding site. Although an alanine scan of 6DBF7 showed that the two cationic groups (lysines) in the partial peptide are crucial to its angiostatic activity, it is the hydrophobic face of the amphipath that appears to interact directly with the surface of gal-1. Based on this structural information, we designed and tested additional DBF analogs. In particular, substitution of the C-terminal Asp for alanine and branched alkyl side chains (Val, Leu, Ile) for linear ones (Nle, Nva) rendered the greatest improvements in activity. Flow cytometry with gal-1(-/-) splenocytes showed that 6DBF7 and two of its more potent analogs (DB16 and DB21) can fully inhibit fluorescein isothiocyanate-gal-1 binding. Moreover, heteronuclear single-quantum coherence NMR titrations showed that the presence of DB16 decreases gal-1 affinity for lactose, indicating that the peptidomimetic targets gal-1 as a noncompetitive, allosteric inhibitor of glycan binding. Using tumor mouse models (B16F10 melanoma, LS174 lung, and MA148 ovarian), we found that DB21 inhibits tumor angiogenesis and tumor growth significantly better than 6DBF7, DB16, or anginex. DB21 is currently being developed further and holds promise for the management of human cancer in the clinic.

Radiation-induced galectin-1 by endothelial cells: a promising molecular target for preferential drug delivery to the tumor vasculature

The present study reports on a new strategy for selective, radiation therapy-amplified drug delivery using an antiangiogenic 33-a.a., tumor vasculature-targeting ligand, anginex, to improve the therapeutic ratio for strategies developed against solid tumors. Our findings indicate that galectin-1 is (a) one of the major receptors for anginex (b) overexpressed by tumor neovasculature and (c) further specifically upregulated in endothelial cells in response to radiation exposure as low as 0.5 Gy. An investigation of [18]-F-labeled anginex biodistribution in SCK tumors indicates that anginex is an effective targeting molecule for image and radiation-guided therapy of solid tumors. An anginex-conjugated liposome capable of being loaded with drug was shown to selectively target endothelial cells post-radiation. The presence of endothelial cells in a three-dimensional co-culture system with tumor cells developed to study tumor/endothelial cell interactions in vitro led to higher levels of galectin-1 and showed a further increase in expression upon radiation exposure when compared to tumor cell spheroids alone. Similar increase in galectin-1 was observed in tumor tissue originating from the tumor-endothelial cell spheroids in vivo and radiation exposure further induced galectin-1 in these tumors. The overall results suggest feasibility of using a clinical or subclinical radiation dose to increase expression of the galectin-1 receptor on the tumor microvasculature to promote delivery of therapeutics via the anginex peptide. This approach may reduce systemic toxicity, overcome drug resistance, and improve the therapeutic efficacy of conventional chemo/radiation strategies.

Human galectin-3 (Mac-2 antigen): defining molecular switches of affinity to natural glycoproteins, structural and dynamic aspects of glycan binding by flexible ligand docking and putative regulatory sequences in the proximal promoter region

BACKGROUND

Human galectin-3 (Mac-2 antigen) is a cell-type-specific multifunctional effector owing to selective binding of distinct cell-surface glycoconjugates harboring β-galactosides. The structural basis underlying the apparent preferences for distinct glycoproteins and for expression is so far unknown.

METHODS

We strategically combined solid-phase assays on 43 natural glycoproteins with a new statistical approach to fully flexible computational docking and also processed the proximal promoter region in silico.

RESULTS

The degree of branching in N-glycans and clustering of core 1 O-glycans are positive modulators for avidity. Sialylation of N-glycans in α2-6 linkage and of core 1 O-glycans in α2-3 linkage along with core 2 branching was an unfavorable factor, despite the presence of suited glycans in the vicinity. The lectin-ligand contact profile was scrutinized for six natural di- and tetrasaccharides enabling a statistical grading by analyzing flexible docking trajectories. The computational analysis of the proximal promoter region delineated putative sites for Lmo2/c-Ets-1 binding and new sites with potential for RUNX binding.

GENERAL SIGNIFICANCE

These results identify new features of glycan selectivity and ligand contact by combining solid-phase assays with in silico work as well as of reactivity potential of the promoter.

Inhibiting tumor growth by targeting tumor vasculature with galectin-1 antagonist anginex conjugated to the cytotoxic acylfulvene, 6-hydroxylpropylacylfulvene

Targeted delivery of therapeutic drugs promises to become the norm to treat cancer. Here, we conjugated the cytotoxic agent 6-hydroxypropylacylfulvene (HPAF) to anginex, a peptide that targets galectin-1, which is highly expressed in endothelial cells of tumor vessels. In a human ovarian cancer model in mice, the conjugate inhibited tumor growth better than equivalent doses of either compound alone. Immunofluorescence on tumor tissue demonstrated that the conjugate, like parent anginex, selectively targeted tumor vasculature and inhibited tumor angiogenesis. Increased activity from the conjugate further suggests that HPAF retains at least some of its normal cytotoxic activity when linked to anginex. More importantly perhaps is the observation that the conjugate abrogates apparent systemic toxicity from treatment with HPAF. This work contributes to the development of tumor vascular targeting agents against cancer in the clinic.

Expression of cathepsin D and galectin 3 in tubular carcinomas of the breast

Tubular carcinoma (TC) is a distinctive type of grade I (G1) ductal carcinoma with particularly favourable outcome and low rate of axillary metastases. To the best of our knowledge, few data are available in the literature concerning the expression of molecules mediating intercellular and cell-matrix interactions in TC. We examined with immunohistochemical methods the expression of galectin 3 and cathepsin D in 17 TC and in 33, 31 and 28 ductal carcinomas of G1, grade II (G2) and grade III (G3), respectively. Results were compared using Chi-square test. Galectin 3 expression was higher in TC than in G1 carcinomas (p<0.05). The pattern of immunostaining was also different with a focal cytoplasmic apical reinforcement in TC. However, cathepsin D stromal and epithelial expression was similar in TC and G1 cases (p>0.05), and lower than in G2 and G3 patients at a stromal level. The higher expression of galectin 3 in TC and its focal staining (apical) pattern suggests that within the group of G1 carcinomas, galectin 3 expression varies according to histological type, and may correlate with prognosis and metastatic potential. We also suggest that cathepsin D could not be involved in neoplastic progression and metastasis in low-grade (G1) ductal breast carcinomas.

Ovarian tumor growth regression using a combination of vascular targeting agents anginex or topomimetic 0118 and the chemotherapeutic irofulven

Combination of chemotherapeutic agents and angiogenesis inhibitors is now commonly employed in the clinic to treat cancer. Here, we used angiostatic agents anginex and 0118, in combination with the chemotherapeutic irofulven, to treat human ovarian tumor xenografts in mice. General linear mixed models were used to statistically analyze tumor growth curves. Overall, combination of a low, non-toxic dose of irofulven with either angiogenesis inhibitor was more effective at inhibiting tumor growth than any of the single agent therapies. For example, the anginex/irofulven and 0118/irofulven combinations inhibited tumor growth relative to controls by 92% (p<0.0001) and 96% (p<0.0001), respectively, with the 0118/irofulven combinations yielding 100% complete responses. This study suggests that combination therapy of 0118 or anginex and irofulven may be highly effective in the clinical setting.

Increased expression of galectin-1 during the progression of cervical neoplasia

Galectin-1, a member of the beta-galactoside-binding family, is widely expressed in epithelial and immune cells. It is involved in several normal and pathologic processes, such as cancer progression, metastasis, and immunobiology. Galectin-1 was found to be overexpressed in various cancer cells and the corresponding benign tissue. Therefore, it has been described as a marker for tumor progression in some malignancies. In the current study, the expression of galectin-1 was examined in 80 formalin-fixed, paraffin-embedded cervical tissues: 20 benign cervical specimen, 20 low-grade squamous intraepithelial lesions (LGSIL), 20 high-grade squamous intraepithelial lesions (HGSIL), and 20 invasive squamous cell carcinomas (ISCC). Immunohistochemical analyses showed that the intensity of the galectin-1 expression on stromal cells next to the transformed cells increased according to the pathologic grade: benign cervical tissue < LGSIL < HGSIL < ISCC (P < 0.001). The epithelial cells were always negative for galectin-1. These results suggest that galectin-1 expression on stromal cells increases with the histopathologic grade of cervical tissues, and it can be concluded that this increase is associated with the progression of cervical neoplasia.

Galectin-1 is essential in tumor angiogenesis and is a target for antiangiogenesis therapy

We describe that galectin-1 (gal-1) is a receptor for the angiogenesis inhibitor anginex, and that the protein is crucial for tumor angiogenesis. gal-1 is overexpressed in endothelial cells of different human tumors. Expression knockdown in cultured endothelial cells inhibits cell proliferation and migration. The importance of gal-1 in angiogenesis is illustrated in the zebrafish model, where expression knockdown results in impaired vascular guidance and growth of dysfunctional vessels. The role of gal-1 in tumor angiogenesis is demonstrated in gal-1-null mice, in which tumor growth is markedly impaired because of insufficient tumor angiogenesis. Furthermore, tumor growth in gal-1-null mice no longer responds to antiangiogenesis treatment by anginex. Thus, gal-1 regulates tumor angiogenesis and is a target for angiostatic cancer therapy.

Nuclear presence of adhesion-/growth-regulatory galectins in normal/malignant cells of squamous epithelial origin

Cellular activities in the regulation of growth or adhesion/migration involve protein (lectin)-carbohydrate recognition at the cell surface. Members of the galectin family of endogenous lectins additionally bind distinct intracellular ligands. These interactions with protein targets explain the relevance of their nuclear and cytoplasmic presence. Expression profiling for galectins and accessible binding sites is a histochemical approach to link localization with cellular growth properties. Non-cross-reactive antibodies for the homodimeric (proto-type) galectins-1, -2 and -7 and the chimera-type galectin-3 (Gal-3) as well as the biotinylated lectins were tested. This analysis was performed with the FaDu squamous carcinoma cell line and long-term cultured human and porcine epidermal cells as models for malignant and normal cells of squamous cell epithelial origin. A set of antibodies was added for phenotypic cell characterization. Strong nuclear and cytoplasmic signals of galectins and the differential reactivity of labeled galectins support the notion of their individual properties. The length of the period of culture was effective in modulating marker expression. Cytochemical expression profiling is a prerequisite for the selection of distinct proteins for targeted modulation of gene expression as a step toward functional analysis.

Decrease of nuclear reactivity to growth-regulatory galectin-1 in senescent human keratinocytes and detection of non-uniform staining profile alterations upon prolonged culture for galectin-1 and -3

Summary Multipotent stem cells (source for interfollicular epidermis, hairs and sebaceous glands) are localized in the bulge region of the outer root sheath of hair follicles, while stem cells giving rise to interfollicular epidermis reside in its basal. Using the multifunctional lectin galectin-1 as a marker to localize accessible binding sites in situ as a step to figure out galectin functionality in stem cells, we studied hair follicle-derived keratinocytes. Specific nuclear binding of galectin-1 associated with expression of DeltaNp63alpha, a potential marker of epidermal stem cells, was detected. Binding of chimera-type galectin-3 to a nuclear site was not found in parallel assays. During the process of ageing in culture when cells acquire properties of senescence, disappearance of the nuclear signal for galectin-1 binding was accompanied by a similar decrease of nuclear DeltaNp63alpha expression and increased binding of galectin-3 to the cell membrane, namely in regions of intercellular contacts. Expression of cytokeratin 10, a marker of the terminal differentiation was seen only in a small fraction of the cell population. These data extend the evidence for nuclear sites with galectin-1 reactivity in squamous epithelial cells, the expression of which is modulated upon senescence. Moreover, the results document the divergence of galectin-1 and -3 on the level of ligand selection in this cell type, underscoring the importance of the technical aspect to employ tissue lectins as probe and to perform a fingerprinting with several markers of the galectin family in parallel.

Comparative phenotypic characterization of keratinocytes originating from hair follicles

The principal pool of epidermal stem cells is located in the bulge region of the hair follicle root sheath. In this research project, we have used a refined procedure to isolate porcine hair follicles including their root sheath and for comparison purposes also human cell material. These cells migrating from the hair follicles were then cytochemically characterized. A panel of antibodies and two labeled plant lectins were tested on cell material obtained under a range of assorted experimental conditions. Due to their role in growth regulation we also studied two endogenous lectins, specifically monitoring their expression and the presence of accessible ligands. These in vitro results were compared with findings on porcine and human hair follicles and human basal cell carcinomas in situ. The keratinocytes originating from hair follicles in the presence of feeder cells are rather undifferentiated and express galectin-1/galectin-1-binding sites but not galectin-3 in their nuclei associated with DeltaNp63alpha positivity. Nuclear reactivity for galectin-1 was rarely observed in the bulge of the outer root sheath of the human hair follicle and of basal cell carcinomas and absent in porcine tissue samples. Exclusion of feeder cells from our cultivation system of porcine hair follicles led to the formation of spheroid bodies from these keratinocytes. Ki67 as a marker of proliferation was not present in the nuclei of cells forming these spheroids. One part of these bodies is positive for markers of post-mitotic differentiated cells, while the other spheroids are composed of poorly differentiated cells, which are able to adhere to feeder cells and form growing colonies. In summary, the detection of galectin-1 and also nuclear binding sites for this endogenous effector points to intracellular functionality of this lectin. It can be considered a potential marker of a distinct cell population, probably at the beginning of a differentiation cascade of keratinocytes.

Tumor galectinology: insights into the complex network of a family of endogenous lectins

Beta-Galactosides of cell surface glycoconjugates are docking sites for endogenous lectins of the galectin family. In cancer cells, primarily galectins-1 and -3 have been studied to date. With the emergence of insights into their role in growth control, resistance to or induction of apoptosis and invasive behavior the notion is supported that they can be considered as functional tumor markers. In principle, the same might hold true for the other members of the galectin family. But their expression in tumors has hitherto been a subject of attention only to a very limited extent. Pursuing our concept to define the complexity of the galectin network in cancer cells and the degree of functional overlap/divergence with diagnostic/therapeutic implications, we have introduced comprehensive RT-PCR monitoring to map their galectin gene expression. The data on so far less appreciated galectins in this context such as galectins-4 and -8 vindicate this approach. They, too, attach value to extend the immunohistochemical panel accordingly. Our initial histopathological and cell biological studies, for example on colon cancer progression, prove the merit of this procedure. Aside from the detection of gene expression profiles by RT-PCR, the detailed molecular biological monitoring yielded further important information. We describe different levels of regulation of galectin production in colon cancer cells in the cases of the tandem-repeat-type galectins-8 and -9. Isoforms for them are present with insertions into the peptide linker sequence attributed to alternative splicing. Furthermore, variants with distinct amino acid substitutions (galectin-8, Po66-CBP, PCTA-1, CocaI/II and galectin-9/ecalectin) and generation of multiple mRNA species, notably those coding for truncated galectin-8 and -9 versions with only one lectin site, justify to portray these two family members not as distinct individuals but as groups. In aggregate, the ongoing work to thoroughly chart the galectin network and to disentangle the individual functional contributions is expected to make its mark on our understanding of the malignant phenotype in certain tumor types.

Expression of galectins in cancer: a critical review

A large body of literature has examined and described galectin expression in cancer. Discrepancies have been observed in the reported data, which hampered clear understanding of the expression profiles. This relates to the use of different types of methods that evaluate either global or specific gene expression in heterogeneous cancer tissue samples, type of antibodies used in immunohistochemistry and procedures of comparison of gene expression. In this manuscript, we review the main data concerning expression of galectins in human cancer. Only galectin-1 and galectin-3, the most abundant and examined galectins, will be examined here.

Expression of galectins in cancer: A critical review

A large body of literature has examined and described galectin expression in cancer. Discrepancies have been observed in the reported data, which hampered clear understanding of the expression profiles. This relates to the use of different types of methods that evaluate either global or specific gene expression in heterogeneous cancer tissue samples, type of antibodies used in immunohistochemistry and procedures of comparison of gene expression. In this manuscript, we review the main data concerning expression of galectins in human cancer. Only galectin-1 and galectin-3, the most abundant and examined galectins, will be examined here.

Glycohistochemistry: the why and how of detection and localization of endogenous lectins

The central dogma of molecular biology limits the downstream flow of genetic information to proteins. Progress from the last two decades of research on cellular glycoconjugates justifies adding the enzymatic production of glycan antennae with information-bearing determinants to this famous and basic pathway. An impressive variety of regulatory processes including cell growth and apoptosis, folding and routing of glycoproteins and cell adhesion/migration have been unravelled and found to be mediated or modulated by specific protein (lectin)-carbohydrate interactions. The conclusion has emerged that it would have meant missing manifold opportunities not to recruit the sugar code to cellular information transfer. Currently, the potential for medical applications in anti-adhesion therapy or drug targeting is one of the major driving forces fuelling progress in glycosciences. In histochemistry, this concept has prompted the introduction of carrier-immobilized carbohydrate ligands (neoglycoconjugates) to visualize the cells' capacity to be engaged in oligosaccharide recognition. After their isolation these tissue lectins will be tested for ligand analysis. Since fine specificities of different lectins can differ despite identical monosaccharide binding, the tissue lectins will eventually replace plant agglutinins to move from glycan profiling and localization to functional considerations. Namely, these two marker types, i.e. neoglycoconjugates and tissue lectins, track down accessible binding sites with relevance for involvement in interactions in situ. The documented interplay of synthetic organic chemistry and biochemistry with cyto- and histochemistry nourishes the optimism that the application of this set of innovative custom-prepared tools will provide important insights into the ways in which glycans can act as hardware in transmitting information during normal tissue development and pathological situations.

Differences in zero-force and force-driven kinetics of ligand dissociation from beta-galactoside-specific proteins (plant and animal lectins, immunoglobulin G) monitored by plasmon resonance and dynamic single molecule force microscopy

Protein-carbohydrate interactions are involved in diverse regulatory processes. To help understand the mechanics and kinetics of dissociation of receptor-ligand complexes, we have analyzed the separation of lactose and the N-glycan chains of asialofetuin (ASF) from three lectins and an immunoglobulin G fraction by surface plasmon resonance at zero force and by atomic force microscopy with variations of the external force. While the (AB)2 agglutinins from Ricinus communis (RCA) and Viscum album (VAA) show structural homology, the homodimeric galectin-1 from bovine heart (BHL) has no similarity to the two plant lectins except for sharing this monosaccharide specificity. The beta-galactoside-binding immunoglobulin G (IgG) fraction from human serum provides a further model system with distinct binding-site architecture. The k(off) constants for the two plant agglutinins were independent of the nature of the ligand at 1.1-1.3 x 10(-3) s(-1), whereas the geometry of ligand and binding site presentation affected this parameter for BHL (0.5 x 10(-3) s(-1) for lactose and 1 x 10(-3) s(-1) for ASF) and IgG (1.3 x 10(-3) s(-1) for lactose and 0.55 x 10(-3) s(-1) for ASF). When assessing comparatively the rupture forces at a loading rate of 3 nN/s with lactose as ligand, 34 +/- 6 pN (BHL), 36 +/- 4 pN (IgG), 47 +/- 7 pN (VAA), and 58 +/- 9 pN (RCA) were measured. For the same loading rate the rupture forces for the receptor-ASF interactions were found to be 37 +/- 3 pN (BHL), 43 +/- 5 pN (VAA), 45 +/- 6 pN (IgG), and 65 +/- 9 pN (RCA). The variation of the pulling velocity revealed in all cases a linear dependence between the rupture force and the natural logarithm of the loading rate. Performing probability density and Monte Carlo calculations, the potential barrier widths, which determine the inverse dynamic dependence with the rate of force elevation, increased from 4 A (RCA) and 7 A (VAA and IgG) to 10 A (BHL) for the receptor-lactose interactions. Presenting ASF as ligand potential widths of 4 A for RCA and IgG and 6 A for VAA and BHL were obtained. Since the dissociation kinetics at zero force apparently cannot predict the behavior in force-driven experiments, these results reveal new insights into biological functions. The dissociation kinetics under force helps to explain the difference in the toxic potency of VAA and RCA and points to a function of the galectin in cis-crosslinking and in transient trans-bridging.

Correlation of Galectin-3/Galectin-3-Binding Sites with low Differentiation Status in Head and Neck Squamous Cell Carcinomas

The accurate determination of levels of differentiation is of prognostic value in human head and neck squamous cell carcinomas (HNSCCs). Because the deliberate selection of biochemical determinants accompanying certain stages of differentiation can refine the predictive power of histochemical assessments, the application of the quantitative evaluation of staining distribution and intensity by computer-assisted microscopy is one prerequisite to potential improvements. We used 2 innovative approaches with peanut agglutinin based on encouraging results with respect to common lectin-histochemistry. First, we used a custom-made neoglycoprotein to monitor the presence of Thomsen-Friedenreich (T) antigen-binding sites. Second, we measured the presence of 2 galectins immunohistochemically and, at the same time, measured lectin-histochemically the presence of accessible ligands for the endogenous lectins. We also monitored the presence of calcyclin, a protein with relevance to cell cycle progression or exocytosis. With 61 cases of HNSCC as their basis, including 31 oral, 20 laryngeal, and 10 hypopharyngeal lesions, the data show that the main modifications observed in connection with a loss of differentiation are related to a modification in the levels of both galectin-3/galectin-3-binding site and T-antigen/T-antigen-binding site expressions. The data obtained also suggest that galectin-3 could act as an acceptor site for the T antigen. Because the level of differentiation is known to be indicative of the recurrence rate in HNSCCs and our data clearly indicate that galectin-3 and the T antigen (and their respective binding sites) are involved in dedifferentiation processes, further investigation is warranted into the roles of galectins in HNSCC tumor progression and recurrence analysis.

The levels of expression of galectin-1, galectin-3, and the Thomsen-Friedenreich antigen and their binding sites decrease as clinical aggressiveness increases in head and neck cancers

BACKGROUND

The aim of this study was to investigate whether an increase in malignancy level is accompanied by significant modifications of the expression of galectin-1, galectin-3, and Thomsen-Friedenreich antigen (T antigen) as well as the expression of binding sites for these three markers in head and neck squamous cell carcinomas (HNSCCs).

METHODS

Immunohistochemical and glycohistochemical staining reactions were carried out with antibodies, labeled lectins, and a custom-made neoglycoprotein on the basis of histologic slides from a retrospective series of 40 normal and 75 HNSCC formalin fixed, paraffin embedded tissues, and were quantitatively described with the aid of computer-assisted microscopy.

RESULTS

Whatever the histologic type, the epithelial tissues in HNSCC exhibited very significantly (P < 0.01 to P < 0. 0001) lower amounts of galectin-1, galectin-3, and T antigen and their respective binding sites than their corresponding normal counterparts. The tumors of the larynx differed very significantly (P < 0.0001 to P < 0.000001) from all the other tumor types. A loss of differentiation in the HNSCCs is accompanied first by the loss of expression of galectin-3 and galectin-3-reactive sites and then by that of the T antigen and its binding site(s). The opposite feature was observed when the parameters associated with the TNM classification were taken into account. The negative lymph node HNSCCs could be distinguished (P = 0.02) from the positive lymph node HNSCCs on the basis of a loss of galectin-3 expression. The modifications occurring in the extent of expression of galectin-1 and galectin-1-reactive sites were relatively marginal in comparison with those observed for galectin-3-dependent and T- antigen-dependent staining.

CONCLUSIONS

The decrease in the extent of expression of galectin-3 and galectin-3-reactive sites, T antigen and T antigen-binding sites, and, to a lesser extent, galectin-1 and galectin-1-reactive sites correlates significantly with an increasing level of clinically detectable HNSCC aggressiveness.

Pulmonary metastases of breast carcinomas: ligandohistochemical, nuclear, and structural analysis of primary and metastatic tumors with emphasis on period of occurrence of metastases and survival

BACKGROUND AND OBJECTIVES

Pulmonary metastases of breast carcinomas have a high frequency and are often subject to surgical intervention. To contribute to advances in the knowledge about morphometric and biochemical parameters of primary tumors and their metastatic lesions, analysis of syntactic structure and thermodynamic aspects as well as of expression of distinct glycohistochemical features with respect to period of metastasis occurrence and patient survival is desirable.

METHODS

Clinical history, surgical findings, histopathological reports, survival of the patients with a maximum follow-up of 15 years, and paraffin blocks of 32 breast carcinoma specimens and their pulmonary metastases were examined. Only potentially curative resections of both the breast carcinoma and their metastases have been included for analysis. The following markers were applied: neoglycoconjugates with histoblood group A- and H-trisaccharides, lactose, alpha-N-acetyl-D-galactosamine and the Forssman disaccharide, a polyclonal immunoglobulin G fraction from human serum with specificity for 9-0-acetylated sialic acid, which is a tumor marker for melanomas, the serum lectins serum amyloid P component and mannan-binding lectin, the mannose-specific plant lectin concanavalin A, and monoclonal antibodies specific for estrogen and progesterone receptors, respectively. In addition, measurements of the integrated optical density (IOD) and tissue structure were performed.

RESULTS

The frequency of expression of hormone receptors and expression of binding capacities to most of the applied probes was similar between the primary and metastatic tumors; however, it varied markedly between different patients. For the IOD parameters, a close association between the primary tumors and their metastases was seen, especially a rather low S-phase-related tumor cell fraction and a high percentage of tumor cells with an IOD >5C. The mean time for the development of intrapulmonary metastases measured 43 months. It was considerably longer in progesterone receptor-negative tumors (49.7 months) and those with a lack of expression of sites with specificity for the Forssman disaccharide (48.7 months). The survival was positively correlated with the presence of binding capacity of histoblood group A-trisaccharide and certain structural parameters, especially the structural entropy and its current. The presence of estrogen and progesterone receptors was not associated with the total survival at a statistically significant level.

CONCLUSIONS

Histochemical features between the primary breast carcinoma and their intrapulmonary metastases can evidently vary. Analysis of the hormone receptor status in metastatic lesions seems to be useful for diagnostic purposes only in rare cases, i.e., distinguishing metastases from primary lung carcinoma. Nonetheless, the survival of patients with metastasizing breast carcinoma is associated with features of the primary tumors, especially the detection of binding capacities for the Forssman disaccharide and the histoblood group A-trisaccharide. Extent of lymph node involvement of the breast carcinoma is not prognostic for later pulmonary involvement.

Animal lectins

Protein and lipid glycosylation is no longer considered as a topic whose appeal is restricted to a limited number of analytical experts perseveringly pursuing the comprehensive cataloguing of structural variants. It is in fact arousing curiosity in various areas of basic and applied bioscience. Well founded by the conspicuous coding potential of the sugar part of cellular glycoconjugates which surpasses the storage capacity of oligonucleotide- or oligopeptide-based code systems, recognition of distinct oligosaccharide ligands by endogenous receptors, i.e. lectins and sugar-binding enzymes or antibodies, is increasingly being discovered to play salient roles in animal physiology. Having inevitably started with a descriptive stage, research on animal lectins has now undubitably reached maturity. Besides listing the current categories for lectin classification and providing presentations of the individual families and their presently delineated physiological significance, this review places special emphasis on tracing common structural and functional themes which appear to reverberate in nominally separated lectin and animal categories as well as lines of research which may come to fruition for medical sciences.

Cell type-dependent alterations of binding of synthetic blood group antigen-related oligosaccharides in lung cancer

Blood group antigen-related oligosaccharides have been implicated in growth regulation, cell mobility control and adhesion; we are therefore interested in the localization of receptors for these oligosaccharides in tumour cells. Labelled neoglycoconjugates that carry synthetic sugar structures are suitable tools to determine: whether such binding sites are present in human lung cancer; whether structural alterations of the glycoligand part will affect extent of binding; and whether cell type-associated alterations can be detected. Sections from 121 cases of lung cancer, representing small cell and non-small cell lung carcinoma, mesothelioma and metastases from extrapulmonary primary carcinomas were used to study the binding of nine synthetic AH- and Le-related oligosaccharides. Probes with fucose-alpha 1-3/4-N-acetylglucosamine-beta 1-R, an A-like disaccharide and 3'-sulfated galactose as ligand appear to bind less well to small cell than to non-small cell lung cancer cases, whereas Lec-disaccharide distinguishes mesothelioma from metastatic carcinoma. The latter ligand, A-like disaccharide and H (type III)-like trisaccharide exhibit evident cell type-associated differences in extent of binding. Thus, tailor-made neoglycoconjugates constitute a promising class of histopathological tools that warrants further study.

Lymphoblastoid cell adhesion mediated by a dimeric and polymeric endogenous beta-galactoside-binding lectin (galaptin)

Glutaraldehyde-polymerized human splenic galaptin, a beta-galactoside-binding lectin, was demonstrated to have enhanced hemagglutinating and asialofetuin binding activity relative to native dimeric galaptin when these lectins were present in solution. The polymerized lectin consisted primarily of 2-, 4- and 12-membered species after reductive alkylation. Both forms of galaptin bound, at 4 degrees C, to saturable B lymphoblastoid cell surface receptors. Estimates obtained by Scatchard analyses, with the binding data expressed in terms of 14.5 kDa subunit molarity, were 5 x 10(7) binding sites/cell with affinity constant Ka = 2.2 x 10(5) M for dimeric galaptin and 17 x 10(7) binding sites/cell with Ka = 3.4 x 10(5) M-1 for polymeric galaptin. Both forms of galaptin adsorbed to polystyrene with high efficiency; however, only plastic-adsorbed polymeric galaptin mediated adhesion of lymphoblastoid cells. Cell adhesion was inhibited by lactose. Plastic-adsorbed polymeric galaptin bound asialofetuin more efficiently than dimeric galaptin. Asialofetuin binding was inhibited 65% and 30-50% by lactose for plastic-adsorbed polymeric and dimeric galaptin, respectively. Native fetuin bound to the adsorbed dimeric galaptin in a lactose-insensitive manner. These data indicate that cell surface receptor-galaptin interaction is carbohydrate specific whereas polystyrene-adsorbed galaptin may demonstrate protein-protein interactions with soluble ligands.

Localization of endogenous beta-galactoside-specific lectins by neoglycoproteins, lectin-binding tissue glycoproteins and antibodies and of accessible lectin-specific ligands by mammalian lectin in human breast carcinomas

Protein-carbohydrate interactions constitute a system of molecular interaction with relevance to pathologic conditions. Carrier-immobilized carbohydrate structures enable the histochemical investigation of the protein part of this recognitive system. However, thorough systematic studies are inevitably required for standardized application of this relatively novel class of markers. Consequently, serial sections of 21 cases of malignant breast lesion were comparatively analyzed with three different types of probe, specific for beta-galactoside-binding lectins. In addition to the chemically lactosylated neoglycoprotein, human lectin-binding glycoproteins, purified by affinity chromatography on resins with an immobilized beta-galactoside-specific lectin, and a lectin-specific antibody were employed to answer the question whether differences occur in their capacity for lectin localization. The patterns of staining were qualitatively similar, the lectin-binding glycoproteins yielding the most intense reaction. Having assured the reliable applicability of the neoglycoprotein, structural alterations of the subterminal carbohydrate residue on the labelled carrier addressed the issue, whether selectivity of binding can be inferred histochemically, allowing rational synthetic tailoring. An N-acetylglucosamine residue in beta-1,3-linkage proved to be a less favorable extension than this type of sugar in beta-1,4-linkage or an N-acetylgalactosamine moiety in beta-1,3-linkage. Binding was clearly reduced in cells of normal breast tissue with this probe. In order to gain evidence on the expression of potential carbohydrate ligands for the glyco- and immunohistochemically localized binding activity, a labelled mammalian beta-galactoside-specific lectin was similarly used as histochemical tool. It effectively bound to accessible sites in the sections. The binding pattern was different to that of plant lectins with specificity to beta-galactosides. This result underscores that caution is necessary in the functional interpretation of results of studies with plant, not mammalian lectins.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of endogenous beta-galactoside-binding lectin as a means to distinguish malignant from benign skin tissue

The immunolocalization of a 30-kd endogenous lectin, referred to as galaptin, was studied in various skin tumor types. Basal cell carcinomas expressed little or no galaptin, whereas nonmalignant basaloid cells, squamous cell carcinomas, melanoma, nevi, and stroma showed more prominent galaptin immunostaining. Therefore, the immunodetection of galaptin may aid the dermatopathologist in difficult histologic diagnosis.

Lactose-binding lectin expression in human colorectal carcinomas. Relation to tumor progression

Lactose-binding lectins having Mr values of approximately 14,000 (L-14.5) and approximately 35,000 Da have been found in a variety of vertebrate tissues, including normal intestine and colon, and in several types of tumors such as colon carcinomas. To determine the clinical relevance of such lectins in human colon cancer, specimens from 46 patients with colorectal carcinoma of identified Dukes' stages were selected and analyzed for the presence and amount of lactose-binding lectins by immunoblotting using a polyclonal, rabbit anti-lectin antibody followed by binding of 125I-labeled anti-rabbit IgG. The amount of a lectin having an Mr value of approximately 31,000 Da (L-31) varied among the specimens. The levels of L-31 lectin in colorectal cancer specimens from primary tumors of patients with distant metastases (Dukes' stage D) were significantly higher than were those from patients without detectable metastases (Dukes' stages B1 and B2). In contrast, among the various specimens the variation in the level of the L-14.5 lectin was smaller, and there was no correlation between the amount of this lectin and cancer stage. Immunohistochemical staining of thin sections of colorectal tumor specimens using antibodies specific for either L-31 or L-14.5 lectin revealed that the two were located at different places, the L-31 lectin primarily within the cytoplasm of carcinoma cells, and the L-14.5 lectin associated with secreted material. These results indicated that the relative amount of the L-31 lectin increases as the colorectal cancer progresses to a more malignant stage.

Human breast carcinoma cDNA encoding a galactoside-binding lectin homologous to mouse Mac-2 antigen

A galactoside-binding lectin (Mr 29,000) has previously been identified in rat, mouse and human tissues. It is an abundant cell-surface component of inflammatory macrophages and their major non-integrin laminin-binding protein. It has also been found in the nucleus of other cell types. Here, we report the cloning and sequencing of a cDNA encoding the human galactoside-binding lectin from a breast carcinoma. The clone encodes a protein of 250 amino acids (aa) that is over 80% identical to its mouse and rat counterparts. The aa sequence has an N-terminal and a C-terminal, 'carbohydrate-binding', domain. The N-terminal domain consists of two parts. The first 41 aa are homologous to a transcription factor, i.e., the serum response factor. The adjacent part (aa 42-106) contains an unusual repeating element, that occurs seven times in human protein compared to nine times in rat and mouse. The C-terminal 'carbohydrate-binding' domain (aa 115-250) shows homology to L-14, another galactoside-binding lectin.

Neoglycoenzymes: a versatile tool for lectin detection in solid-phase assays and glycohistochemistry

Carbodiimide-mediated coupling of p-aminophenyl glycosides to a naturally nonglycosylated enzyme yields a neoglycoenzyme. This compound combines inherent enzymatic activity with synthetically conferred ligand properties to lectins. Appropriate choice of the ligand allows custom-made synthesis to reliably detect various types of lectins. To exemplify practical applications of this class of compounds, glycosylated bacterial beta-galactosidase has been employed to quantitate plant lectins, immobilized on plastic surfaces as well as on nitrocellulose. Competitive inhibition by specific sugar ascertained the dependence of binding on protein--carbohydrate interactions. In view of lectins as tools, a sandwich lectin-binding assay for high mannose-type glycoprotein detection has been modified to principally facilitate wide application to other lectin-reactive sugar chains by introducing the neoglycoenzyme. In addition to lectin determination in solid-phase assays, neoglycoenzymes allow one to glycohistochemically localize endogenous lectins in tissue prints and tissue sections with a minimum number of steps. This nonradioactive, rapid, sensitive, and convenient assay concept, based on conjugation of a ligand to an enzyme with maintenance of its receptor-binding activity, may find extended application beyond lectinology in receptor analysis.

Mapping of receptors for carbohydrate constituents of glycoconjugates in well-differentiated and malignant ependymomas: a glycohistochemical study

Recognitive interactions between the carbohydrate part of cellular glycoconjugates and endogenous receptors supposedly govern important biological processes. Consequently, their elucidation can be of considerable value in tumour diagnosis. The histochemical patterns of expression of endogenous sugar receptors (e.g. endogenous lectin-like proteins) of 10 cases of well-differentiated ependymoma and 10 cases of malignant ependymoma were analysed, using a panel of 18 biotinylated (neo)glycoproteins and a standardized staining protocol. Within this panel, differences in the extent of staining for intracellular sugar receptors in well-differentiated and malignant ependymomas were histochemically detectable. In comparison to the well-differentiated ependymomas, the anaplastic form of the tumour exhibited a generally higher capacity to specifically bind labelled (neo)glycoproteins, containing alpha- or beta-glucosides and a disaccharide, characteristic for one type of beta-galactoside-terminated chain structure of glycoproteins. A significantly reduced binding was seen for tumours of the anaplastic type with labelled markers, carrying histochemically indispensable glucuronic acid residues. These findings suggest that labelled neoglycoproteins are a valuable tool for assessing the endogenous sugar-binding capacity in diagnostic histopathology. Our descriptive analysis of endogenous sugar receptors may also be a rational basis for studies on the functional significance of changes in the expression of their endogenous ligands and the cellular glycoconjugates. Further investigations are also possible on the correlation between the degree of differentiation and expression of both parts of a recognitive system, based on protein (receptor)-carbohydrate (ligand) interactions, in tumours of the central nervous system, especially ependymomas.

Is part of the molecular basis of the perineurial barrier function the lack of endogenous carbohydrate-binding proteins?

The sugar part of cellular glycoconjugates and specific endogenous sugar receptors, i.e., lectins, can establish a system of biological recognition based on protein-carbohydrate interactions. An assortment of labelled (neo)glycoproteins, carrying different types of sugar moieties, is synthesized to localize respective sugar receptors. With these tools, the histochemical patterns of endogenous carbohydrate-binding receptors of the epi-, peri-, and endoneurium were analyzed in human sural and accessory nerves and in swine sciatic nerve. This approach is complementary to the application of plant lectins, focusing on endogenous carbohydrate-binding proteins (lectins). In contrast to the epi- and endoneurium, which bound certain types of carbohydrates, such endogenous sugar receptors were histochemically not detectable in the perineurial cells. Moreover, no histochemical reaction was present in the "connective tissue septa" localized in the endoneurium in which the endoneurial vessels were embedded. This common property supplies evidence that these septa are composed of perineurial cells. They may represent a barrier in addition to the capillary endothelium. Our observations suggest histogenetical differences between the cell populations of epi- and endoneurium vs. perineurium. This significant difference in the ability to bind carbohydrate residues, conjugated to a carrier protein, is contradictory to the assumption that perineurial cells and fibroblasts are functional variants of the same cell type. The histochemical patterns of endogenous carbohydrate-binding receptors found in human and swine nerves were similar but not identical, with exception of the perineurium, reflecting phylogenetic differences in the expression of sugar-binding proteins. The absence of specific sugar receptors in perineurial cells, however, seems to be a more general phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)